As catalysts to be present in the reaction system that 1-olefines as starting materials are isomerized to inner olefines having their double bond in the inner side of their molecular chains, there has been known acids and bases (metals), specifically inorganic acids such as sulfuric acid, phosphoric acids, etc., alcoholates, sodium, potassium and the like (Yuki-gosei-Kagaku, 874, 30 (1972)).
However, when inorganic acids are used, a large amount of polymers of 1-olefines are formed as by-products and the control of isomerization reaction is difficult. On the other hand, metal catalysts or catalysts bearing metals on carriers having a large surface area such as alumina, silica gel, activated carbon, etc. (e.g. Journal of American Chemical Society, 82, 382 (1969)) have high catalytic activities, but they can cause firing by exposure to air or absorb moisture to become inactivated, therefore being inconvenient in handling.
Japanese Patent Kokai Publication No. 62-39582 describes using solid acid-base catalysts including silica/alumina/iron types and silica/titania types as isomerization catalysts. Japanese Patent Kokai Publication No. 63-135596 describes using mordenite as an isomerization catalyst. However, the former tends to form self-polymers of 1-olefines at a high rate and further, both of the former and the latter exhibit a low reactivity of 1-olefines, therefore being left the problem that they can not increase the overall yield.
The inventors performed various investigations to dissolve the above problems involved in the preparation of inner olefines having their double bonds in the inner sides of their molecular chains by isomerization of 1-olefines as starting materials, and have eventually found out that the use of mordenite-type zeolites as a catalyst to be present in the isomerization reaction system and the control of reaction conditions to a specific state can inhibit self-polymerization of 1-olefines to thereby obtain isomerized inner olefines at a high yield and additionally that the above process is excellent in catalyst stability, thus accomplishing the present invention.